Recalling the Big One: Not WW II, The Great Leaning War

It seems like a lot longer, but about 12 years ago-circa 1996-the Great Leaning War was fought. If you don't own a high-performance single, you may not have been a combatant and even if you do, you may have chosen wisely to remain on the sidelines.

The short summary is this: George Braly, then and still a Bonanza owning lawyer and aeronautical engineer, wondered why the IO-520 wouldn't run smoother when leaned. His investigations re-discovered what the late Continental engineer Carl Goulet had known for years: the log-and-runner induction system on these engines had some air flow oddities that complicated fuel/air distribution such that some cylinders ran richer (or leaner) than others. Braly's idea was to micro tweak the fuel injection nozzles to balance the gas to the air and thus was born GAMIjectors, of which some 18,000 sets have been sold.

As GAMIjectors took off, Braly further discovered-make that re-discovered-that engines ran at peak efficiency and were cooler and cleaner when flown on the lean side of peak EGT/TIT. Continental knew this, because they authorized lean of peak operation for the Piper Malibu in 1984. Any 10th grade physics student can grasp the science with a few minutes spent studying the EGT, CHT and cylinder pressure curves that have been out there since God created dirt, or at least relatively accurate temperature and pressure instruments.

But a reasoned and calm understanding was not to be. Lycoming objected-and still objects-to lean-of-peak operation, claiming that it of itself is not harmful, but owners lack the instrumentation to do it correctly. Somehow the multi-probe engine monitor and, lately, MFD engine analytical pages the size of a small television, escaped them. Continental has run hot and cold on the idea, but most of the engines it sells for high-performance airplanes are factory blessed for lean of peak. None of Lycoming's are, although some owners do it anyway.

The airport couch-rat chattering class and no small number of mechanics blindly resisted LOP. You'd burn your valves. The engine would run too hot. Some kind of mysterious chemical reaction would erode the exhaust manifold. You'd void the warranty. Hair would grow on your palms. Never mind that there was no science or engineering to support any of this. Some mechanics who are absolute geniuses at bending metal and bringing spark and fuel together to create the magic of internal combustion are absolute idiots when it comes to understanding that combustion.

Clearly, owners had to be educated in the hopes of bringing their mechanics along. Braly and two early acolytes of GAMIjectors-John Deakin and Walter Atkins--put together Advanced Pilots Seminars, a series of weekend courses designed to school discerning owners in the finer points of engine operation and leaning. And thus went forth across the land a new understanding of leaning based on actual science, not engine manufacturer reactionism or mechanic hideboundedness.

After a few years, APS stopped the course because, as Walter Atkinson likes to say, "we won." And given that every new Cirrus SR22 turbo exits the factory with a POH more or less requiring lean of peak operation, he's not exaggerating. Yet still, a decade later, there are pockets of resistance.

I periodically fly new airplanes for product review purposes and I'm occasionally surprised at how poorly some demo pilots have this leaning thing down. At Cirrus, they're all over it-you'd expect that. Less so at Mooney and Cessna. I'm still occasionally told that "this lean of peak thing runs the engine too hot." There was a time when I'd put my flight instructor hat on, draw the little CHTs and EGT curves and try to explain how it really works. I don't do that anymore. As my boss says, we're not running a school for boys.

But APS is and they still occasionally offer the weekend course. George Braly emailed me this week to say the next one is scheduled June 20 to 22. Check APS's site for the details. (www.advancedpilot.com)

What's curious about any resistance to lean-of-peak operation is that it exists in a world where avgas is $5 or more a gallon. If you could run your car the same way you run your airplane lean, you could increase fuel economy by about 20 percent. Who wouldn't do that? Well, some people to whom high gas prices don't matter aren't interested in lean of peak and don't want to suffer the slight speed penalty associated with it. Fair enough-at least the argument isn't based on some phony claim about burned valves.

Out of curiosity, I asked Braly how much total fuel savings GAMIjectors and lean of peak could conceivably be responsible for. "Current estimate is that there are about 18,000 GAMIjector kits and that at 125 hours/year, that amounts to about 2,250,000 hours annually." Owners who run rich of peak may save about 1.5 GPH, while lean of peak on large displacement engines drops the fuel burn by 2.75 GPH. That's a total of 6.2 million gallons a year or more than $30 million a year at current prices.

That's a big number. Moreover, for the individual owner flying a modest 125 hours a year, the payback on a $750 set of GAMIjectors used to be about a year and a half. Now it's six months. Not bad for set of hardware you can hold in one hand.

Comments (49)

You're oh so right. I have had Gamijectors/JPI700 in my 1970 A36 for 7 years. They are fantastic and do everything it says they'll do on the box. I too used to fight the good fight and draw diagrams for other pilots and engineers but these day rarely do. All my aeroplane owning friends are converts and those people I still occasionally meet who are resistant can only be described, after 12 years, as 'thick'. I just don't have the energy to waste my time selling the self evident anymore.

My IO-470 Bonanza just doesn't seem to like LOP. I ease the EGT past peak to about 50-75 degrees and the engine runs rough. I'm supposed to have GAMIs (I just bought the airplane in February), so what's the problem?

We had an IO-550G in a kit plane (Express) which we routinely ran lean of peak. It ran fine, never had any problems. The tuned intake engines (such as in the Cirrus) do very well in this mode. Can"t see any reason th cool an engine with fuel when you can use air.

I have a Mooney 201 with a turbo. I have been running it LOP for about 4 years and 800 Hrs. Seems to run fine. Saves about 10% in fuel for the same TAS. It runs nice and smooth with stock injectors. I can still read the dipstick through the oil after 50 Hrs. You can't do that running ROP. I used to fly a friends Rockwell 112TC when my plane was down. I could never get that thing to run LOP; it would start coughing and sputtering at about peak EGT. I don't think carbureted engines do as well LOP.

I ran an IO-520K in a Super Viking for 1000hrs most of those hours with GAMI's and found that LOP it very unhappy even after retuning the injectors twice. It turned out that the fix was to richen 6 of the injectors and replace the mags and finally it worked. But I usually fly above 8000 ' anyways so I ran 25 ROP with excellent results in speed vs fuel burn with no loss of airspeed. My oil at 50 hrs looked very clean, to the mechanic's amazement!

I fly a naturally aspirated Bonanza and try to fly above 8000' whenever possible. 9000' and 1000' give best TAS and lowest fuel burn. I lean to the engine stumbles a bit and then push the mixture in 3/8".

I got lucky with the carbureted Lycoming O320 in my Warrior. Runs very well LOP, I can lean to about 75 degrees lean before roughness starts and one of the cylinder EGT's drops way down (misfiring). I usually cruise-lean by doing the big mixture pull and adjusting for 8GPH fuel flow (which works out to about 30 degrees LOP. Still get about 125KTAS at 3000ft (even better higher up), not bad speed and great economy. Sometimes if I'm going for really economical, like 7.5GPH, I close the throttle slightly and add a smidge of carb heat to keep it smooth. CHT's nice and low in the low to mid 300's, EGT's high as expected (close to 1500).

The article talks about "pockets of resistance". I fly airplanes that are serviced at 6 different shops in New England. Every mechanic in every shop still resists lean of peak and the most common comment that I hear is, "It will burn a hole in the tops of cylinders." I assume that this is probably caused by improper leaning procedures, in actuality, but it's very hard to argue with their "logic". Until the A&Ps are educated about proper lean of peak operations, Gamijectors will be fighting an uphill battle.

Also, when I suggest to an owner that they get Gamijectors, then they talk to an aircraft or engine factory representative who tells them that installing the new injectors will void the warranty, it becomes nearly impossible to convince the owners that this will save them money. Aviation Consumer has done a great job of convincing their readers but educating the manufacturers & mechanics would go a long way toward improving the industry.

No one has mentioned the effect of excess O2 at the very high temperatures of exhaust gas. Is this a cause for concern? Intuitevly it seems that excess oxygen roiling around in a hot cylinder and going by hot exhaust valves could cause damage.
Anyone care to comment on this?

I bought my Bonanza with 800 hours on the IO-520 12 years ago and added the GAMIs and JPI700 and began flying lean of peak. Over 1000 hours later my mechanic insisted I get an overhaul. When Bill Cunningham at Powermaster tore down my engine, he said the cylinders met service limits, the crank shaft met factory new limits, and it was the cleanest engine he had ever torn down. I now have over 500 hours on the re-built engine. That's 1500 hours of LOP operation and never a cylinder pulled. I was flying at 7000ft yesterday (a 95F day) at 73% power and my cylinder temps ranged between 330-357F. That's why the oil is always clean and honey looking. But I'm still told by some that I'm going to butn up my engine.

I started running LOP when Deakon wrote about here on Avweb, what, nearly a decade ago? I have not had an engine problem yet and I run 3 gph less than "book" at 75% and since I have a turbo there is no speed penalty at all. Well over 2,000 gallons saved now not to mention al the other benefits to my engine.

Thanks Deak and Avweb for those wonderful articles.

(Paul, you ought to re-introduce that series of excellent articles just in case there a few open minded readers out there who have not gotten the word)

The comment about excess O2 is a bogus comment. Whether the engine is running at an acceptable temperature, below 380 degrees, the components don't know the difference between a rich of peak 380 degrees or a lean of peak 380 degrees. The visible difference is fuel flow and if the engine is inspected and/or the oil changed the oil will be much more dirty ROP vs LOP and the carbon build on the valves and pistons will be much greater ROP. The burn is much more complete LOP vs ROP so the oxygen remaining may well be greater ROP!

"The comment about excess O2 is a bogus comment"
Not a "comment". A question.
Hoping someone will address what seems to be an intuitively obvious concern.
ROP by definition means there is more fuel than O2. The O2 is all used during the burn up when ROP. Thus the unburned soot.
LOP on the other hand -by definition- means more O2 than fuel and therefore some 02 left over after the burn. This still seems a concern at CHT and EGT temps. Any welder knows what an oxidizing flame does to metal. My question is: can it be a problem at the temperatures found in an aircraft engine? exhaust.

I would love to run LOP with my I0-470-N (P35 Bonanza). Problem is, I don't (yet) have GAMIs and I don't (yet) have a multiprobe analyzer. Until I get them, does anyone know of a safe way to run LOP? I do have a three probe Alcor EGT, but only a single probe CHT, which never seems to move much no matter what the mixture is. I try to lean to engine roughness and then enrich slightly, but frankly the engine is very smooth and the point of developing roughness is hard to pinpoint.

With a turbosupercharged engine, you have to be a little more careful, as peak temp operation is a little hard on the exhaust system. On the other hand, at altitude without forced induction you can lean until the engine quits and it will still not do any harm (just won't make much power)

Robert Johnson wrote "(Paul, you ought to re-introduce that series of excellent articles just in case there a few open minded readers out there who have not gotten the word)"

Actually, guys & gals, John Deakin's "Pelican's Perch" engine articles (24 of them grouped together) are still availble on AvWeb. Great educational material written in a most entertaining way; DON'T MISS THEM!

Work your way thru the menus: Go to NEWS>, COLUMNS> (see right sidebar under Active Colums)>, PELICAN'S PERCH>, go to INDEX (at bottom of page)>, again, see right-hand sidebar, click on "Engine related columns"; all 24 titles will apppear. I've got that bookmarked. Love to study this stuff at liesure 'cause it takes more than simply reading once to absorb it all. Take your time and enjoy!

One loser, one winner (carbureted):
LOSER - Had an O-540 that was so spread out that 1&2 would run LOP, 3&4 at peak, and 5&6 ROP. There was no way to even it out (butterfly angle, carb heat, whatever). During teardown, pistons 1&2 were spectacular clean golden brown, 3&4 were smudgy, and 5&6 were so gunged up with crud that they almost could not be removed from the engine.
WINNER - an O-360 that will run LOP with less than 50 degrees CHT and 100EGT on all four. Can't do it at all power settings, and it is less cooperative at partial throttle, but I can generally find a sweet spot for whatever speed/power I'm interested in. At least a 15% savings at 50 LOP, and not even a 3-knot penalty.

One advantage that nobody's mentioned yet is: little or no CO in the exhaust when running lean. Complete combustion results in mostly CO2 with very little CO, while lots of CO results from incomplete combustion. Seems safer for the cabin occupant(s) in case there should be a muffler crack into the heating shroud.

Excess oxygen: To cause oxidation there has to be something to react with. Excess oxygen after combustion exists in an environment with no oxydizing agents, so how could that lead to a hole in a cylinder? You've got lower cylinder temperatures than in ROP regime and the fuel-air charges at the bottom of each stroke have nothing left to burn in them.

The biggest real danger with LOP operation is detonation, hence the need for a multi-probe engine monitor for both EGT and CHT, so you can keep all cylinders safely on one side or the other of peak EGT. You have to run rich on one side of the detonation danger zone, or lean on the other side of it. It's the middle range, close to peak EGT, where the danger is, at least until you reach a certain altitude in normally aspirated engines and they can't develop sufficient power for detonation to be a concern.

Local Mechanic -- Korean war vintage -- runs an older 182 lean of peak with carb heat on. He will walk around the airport and point out engines where you can and can't run lean of peak, based on the intake manifold. He says running carburetors LOP was common in the Pacific theater during WWII. FWIW

I fly a 1994 A-36 with an IO-550 that the previous owner was kind enough not to fly enough to keep it from becoming corroded, so I have a nice new Millenium Overhaul and GAMIs.

I couldn't get the thing to run lean of peak to my satisfaction until going to BPPP in March. My instructor did a great job of demonstrating LOP operations. ROP at 21" MP and 2300 RPM I turn 150 Kts IAS at 8,000 feet on 17 gallons an hour. Or LOP 21" MP and 2300 RPM I turn 145 Kts at 8,000 feet on 11 gallons an hour.

EGT are the same 1375F on the hottest cylinder. CHT's are a solid 20-25 degrees cooler when running LOP.

One thing no one mentions is the higher nitrous oxide emissions at LOP (which is why cars can't do it). I hope no one works for the EPA who reads this! Catalytic converters and EGR valves on airplanes would be an impractical headache, but would force the issue of electronic engine management!

Without engine monitor:
The advice is to lean per engine and airframe manufacturer instructions. Attempting LOP without knowing what the CHT's and espectially EGT's are doing is dangerous. With some engines they allow you to run right at peak EGT if you're above a certain altitude (and therefore below a certain max power), and in those cases you could experiment with LOP all you want. At high power settings LOP is extremely dangerous unless you know what the temps are doing.

GAMI:
These aren't always necessary on fuel-injected engines. They balance the fuel distribution and thereby lessen the temperature spread between cylinders, which is critical to LOP (to be able to get to the lean side with all cylinders before any of them get fuel-starved and misfire). Some injected engines happen to already have a good enough balance and don't need GAMI's. Some smaller (4-cyl) carbureted engines also have that magic mojo and can do LOP as well, due to their simple and balanced manifold designs.

"Excess O2" is not a concern, it's not even real. Even LOP, exhaust is O2-poor. Air is about 20% O2, at peak EGT you'd burn essentially all of it. If you reduce fuel flow by 10% from peak EGT (which is a LOT), you'd still burn 90% of the O2, leaving exhaust that's just 2% O2, while there's 10 times as much in the air on the outside of every hot exhaust pipe, LOP or ROP, without damage. The corrosive compounds in exhaust are from the fuel so running ROP to prevent "excess O2" makes things worse instead of better.

Okkay...now, for those of us with multiprobe engine monitors and carbureted engines, what should we do? I just took delivery of a new AMD Zodiac XLi today, and it's got EGT and CHT on all four cylinders, and a carbureted O-200. I'm going to run it per AMD's recommendations (lean to no higher than 1380 F EGT on the hottest cylinder) during the first 50 hours, but then what? Even if it'll just cut 6 GPH to 5, it's still worth it.

On the Zodiac I would fly it at high power initially (say the first 5-10 hrs, look for the oil consumption to stabilize and change to a detergent based oil) and full rich in climb and like they said don't lean much for the first 50 hrs.
The GAMI school will say don't run it in the never never zone of 100 ROP to 50 LOP below 8000' or approx 20 inches of manifold pressure. Once you reach 8000' you can run the mixture where ever you like. For best speed I would run 25 ROP (rich of peak). Each day the peak may be vary as air density changes. If it will operate smoothly LOP you are good to go to that setting at any altitude, make sure all cylinders are at least 50 LOP and you should see all cylinders cool down. The max for long life is 380F or less, if the cooling system is well designed you should see most cylinders 350F or less.

"leaving exhaust that's just 2% O2, while there's 10 times as much in the air on the outside of every hot exhaust pipe, LOP or ROP, without damage"

Well, that isn't quite true. Lets not forget our elementary gas law physics. The PARTIAL PRESSURE of the unburned O2 will be quite a bit more than the 2% supposed above. Also, the PARTIAL PRESSURE of O2 on the -outside- of the exhaust stack will be less than at sea level as the airplane is typically at cruise altitude during the leaning process. Thus a huge difference exists between what is happening on the inside of the cylinder under the pressure and temperature of combustion. My question has not been answered yet:
Is there an oxidizing flame inside the cylinder under these conditions?

Whether you go by mass, partial pressure, or any other measure, an LOP-operated engine is being cooled by excess [u]air[/u] not pure excess O2, and the amount of overall absolute excess O2 is relatively tiny. An oxydizing flame would require a much, much, much larger quantity of oxygen per unit of exhaust gas.

Empirical evidence (i.e. the facts) support the theory. Exhaust parts are cleaner and last longer when the engine is run LOP, with less corrosion. So there is clearly not an oxydizing effect from the excess O2 in the exhaust gas.

I would talk to GAMI on the B36TC, I just asked about buying one and running it LOP, Tim Reohl said it is not a good candidate for LOP operations,in fact he owns one that has been converted to an IO-550 Turbo-Noramlized (you can read all about it on their website tornado alley .com) the IO520 will usually run rough due to poor fuel distribution characteristics of that particular combo from TCM.

I fly a Bellanca Viking with a IO520 with gami's and a JPI700. I just started to run some tests. at 5,500 ft at standard temp plus 11deg f., at 65% power, I showed 11 1/2 gph @ 50 deg lean of peak. The same power setting at 30 deg rich of peak showed 14 gph (on a pressure type ff meter). The engine ran very smoothly, but there was a noticable loss of power when running LOP. My question is this: I read in the posts above about some folks running LOP at 75% power. My mechanic feels that detonation is possible above 65% and that this could cause extensive damage before it could even be detected. I have heard this from other sources. Any thoughts?

Regarding detonation at high power settings: there is a danger zone surrounding peak EGT at high power settings. However, even at 75% power if you are well LOP (50 degrees is certainly enough) on all cylinders you are outside that range. Looking at the graph (there are 2-3 versions of the graphs out there, including some in John Deakin's Pelican's Perch articles on the subject on AvWeb), the detonation danger zone (approximate) at 75% power is from 180 degrees rich of peak to 35 degrees lean of peak.

The partial pressure of the O2 in THE EXHAUST PIPE I referred to, a tube open at one end, will be quite a bit lower than the outside atmospheric at SL, which hot engines tolerate quite easily for a long time. Indeed, engine corrosion is commonly traced to lack of use/infrequent oil changes rather than the effects of use, either LOP or ROP.

As for the cylinders, to avoid the pressures at peak EGT we have to choose between ROP or LOP so our only choices are to have either unburned O2 or unburned hydrocarbons. Speculation aside, is there any evidence that unburned hydrocarbons are less corrosive than unburned O2?

ROP I have seen with my own eyes builds carbon that causes damage to valves (pitting), stuck rings, and can be the cause of detonation, (glowing pieces of carbon). LOP or Oxidation damage has not been seen by anybody I know in the engine business rather they see super clean internal parts and unusually low wear rates compared to the ROP. Remember there are 13,000 engines that have been rejetted with GAMI's there are 600 Turbo-Normalized engines that have converted, there are close to 1000 Cirrus Turbos and several hundred Columbia 400's all running with no outcry as to damage by LOP operations. Diesel engines, and every turbine aircraft engine or other turbine runs LOP by about 20%, the only time they can have a threat of damage is as they richen closer to Peak EGT. When hotrodders modify diesel pick-ups they richen the fuel mixture and that is when the failures begin to happen.

On days with high temperatures I have found the only way to keep CHT below 380 in the climb phase is to run LOP. Using factory settings will quickly have CHT above 390, even with airspeed >110 and a reduced climb. My airplane is a 1990 F33A with Gami injectors, and about 2200hrs on the original motor.

FILL CEE - for a guy with 2200 hrs on the original motor I'd be the last to suggest any other procedure than that being used. But assuming good baffles, full rich mixture and proper timing, I do wonder why you cannot keep CHT below 380 unless operating LOP. Low FF during T/O & climb would certainly be suspect. Any FF that will not keep EGT at or below 1300dF during WOT climb indicates FF too low for proper cooling - you do climb wide-open throttle, do you not? If so, you should see FF in the neighborhood of 28 gph. If much lower, turning the Aux fuel pump ON and adjusting mixture accordingly provides a temporary solution to providing enough cooling fuel ROP.

I agree, my engine was overhauled (we put Millennium II cyclinders on) and I suddenly realized on takeoff and climb I was seeing 1450F on average with 24.4 gph (factory spec). It took several adjustments to get it cooled down to 1260F @ 31 gph. I still had to use low boost sometimes on cool days where the air density was high, but cylinders temps would never exceed 350F vs 400F before the enrichment. I find so many mechanics have no clue about this area of fuel requirements to keep an engine healthy. I had to insist on the adjustments.

Why is everybody talking to there mechanics about how to run their engines. Mechanics don't normally run engines except to warm them up and test them after re-assembly. I have an A&P license and there was very little training with regard to this subject. As a pilot I have hour upon hour to twiddel with the controls and see how the engine responds. As an airplane owner I can watch my engine very carefully over time, knowing exactly how it is operated. A mechanic can only go on second hand information about how the engine is operated and may only see the engine once or twice a year.

Hear, hear. The average mechanic probably doesn't know much about the chemistry or physics involved in engine operation, either, so why should a mechanic be any authority on the ROP vs. LOP debate (at least any more than the average somewhat informed pilot like myself :) )?

I must disagree with the B36TC comments running LOP. I have a 1992 B36TC with FACTORY tuned injectors. Not sure when they started this but I had a factory reman put in about 4 years ago. It run beautifully at LOP. At 12k feet, I run 15GPH (3 gallons savings) and 25-50 degrees cooler LOP. I will be happy to demonstrate this to anybody whose says a B36TC won't run LOP. I think the GAMI's are great but my plane didn't need them.

Just go to the GAMI website, the graphs are there for normally aspirated engines.They wiil to tell you to run the EGT'S anywhere you wish above 8,000' I usually run 25F LOP at 8500 and above. Below those altitudes you run full manifold pressure and all cylinders 50F LOP or leaner. The never never area is from 100 ROP to 50 LOP. You will see the red zone indicating this on the graph.